MRI Contrast agents

Category: Medicines

Type

Involuntary

Introduction and description

 

MRI contrast agents are a group of contrast media used to improve the visibility of internal body structures in magnetic resonance imaging (MRI). The most commonly used compounds for contrast enhancement are gadolinium-based.

Such MRI contrast agents shorten the relaxation times of atoms within body tissues following oral or intravenous administration.

In MRI scanners, sections of the body are exposed to a very strong magnetic field causing primarily the hydrogen nuclei ("spins") of water in tissues to be polarized in the direction of the magnetic field. An intense radiofrequency pulse is applied that tips the magnetization generated by the hydrogen nuclei in the direction of the receiver coil where the spin polarization can be detected. Random molecular rotational oscillations matching the resonance frequency of the nuclear spins provide the "relaxation" mechanisms that bring the net magnetization back to its equilibrium position in alignment with the applied magnetic field. The magnitude of the spin polarization detected by the receiver is used to form the MR image but decays with a characteristic time constant known as the T1 relaxation time.

Water protons in different tissues have different T1 values, which is one of the main sources of contrast in MR images. A contrast agent usually shortens, but in some instances increases, the value of T1 of nearby water protons thereby altering the contrast in the image.

Effect of contrast agent on images: Defect of the blood–brain barrier after stroke shown in MRI. T1-weighted images, left image without, right image with contrast medium administration

How it works

Why do people get hallucinations from MRI contrasting agents? - because they do as the observations show.

Gadolinium(III) containing MRI contrast agents (often termed simply "gado" or "gad") are the most commonly used for enhancement of vessels in MR angiography or for brain tumor enhancement associated with the degradation of the blood–brain barrier.

For large vessels such as the aorta and its branches, the gadolinium(III) dose can be as low as 0.1 mmol per kg body mass. Higher concentrations are often used for finer vasculature.

It is the compromised nature of the blood brain barrier which may be key, or even the fact that it is not known the blood brain barrier has been compromised.  Aluminium has now been shown to attack the blood brain barrier and by doing so may have compromised the barrier far more than is realised.  The very damage done is probably responsible for the entry of whatever pathogen is attacking the brain.  Thus it is too easy for these agents to pass into the brain at much higher quantities than realised.

In theory Gd(III) chelates do not pass the intact blood–brain barrier because they are hydrophilic. Thus, these are used in enhancing lesions and tumors where the blood-brain barrier is compromised. But again, if the damage is severe, they may leak through. 

The other option is simply that these substances are toxic to the body and toxins can cause hallucinations anway.

References and further reading

Observations

The following total figures were derived from the eHealthme site [and the observations below], which record the Adverse drug reports submitted by doctors to the FDA and SEDA.  The figures only apply to the USA and were correct as at January/February 2016.

Related observations

Hallucination

• Anaphylaxis to drugs 025498
• Gastrografin 019904
• Magnevist 019906
• Omniscan 019804
• Optimark 019812
• Prohance 019868
• Ultravist 020246
• Ultravist and Iopromide 019905

In time

Synaesthesia, Pure or enhanced perception, Inter composer communication, Vision, Dream, Perception recall, Exploring group perception

• Danielou, Alain – On drugs you are possessed by the spirit being of the drug 022582